1. Field of the Invention
The present invention relates to a method for focus adjusting and a camera in which focus evaluation values are calculated based upon image-capturing signals output from an image-capturing device and the focus of a photographic lens is adjusted so as to achieve the highest focus evaluation value.
2. Description of the Related Art
In an electronic camera that captures a subject image with an image-capturing element such as a CCD, a focus adjusting method whereby a high-frequency component corresponding to the contrast signals in the image-capturing signals is extracted and the focus lens is moved to a lens position at which the high-frequency component is at the highest level is adopted in the related art. The high-frequency component is referred to as a focus evaluation value and the focus adjusting method described above is referred to as a hill climbing AF.
Normally, the focus lens is caused to move over part of or the entirety of its drive range and the focus evaluation value is obtained at various lens positions in order to calculate the lens position corresponding to the maximum focus evaluation value. As long as a sufficient number of focus evaluation values are obtained relative to the extent of the lens drive range, the highest focus evaluation value is selected and the focus lens is moved to the focus match lens position at which the highest focus evaluation value is obtained.
If, on the other hand, the focus evaluation values cannot be obtained in sufficient numbers, the focus match lens position at which the focus evaluation value is assumed to indicate a substantially highest level is calculated through an interpolation operation (interpolation method) (e.g., a 3-point interpolation operation) or the like. The focus match lens position is calculated through the interpolation operation by using the highest focus evaluation value and at least focus evaluation values at positions preceding and succeeding the position corresponding to the highest focus evaluation value. In this method, the accuracy of the interpolation operation improves as the number of sets of data used in the calculation increases.
However, if the highest focus evaluation value is obtained at a focus evaluation position that is closest to an end point of the lens drive range, the focus evaluation value at the position either preceding or succeeding the focus evaluating position corresponding to the highest focus evaluation value is not available. This gives rise to a problem in that the focus cannot be adjusted with accuracy when the focus match position is present near an end point of the lens drive range.